*I

a

Universi ty Studies 495-B North Carolina S t a t e University Apr i l 25 , 1983 Quin t M. Barefoot

POLLUTION PREVENTION ALTERNATIVES I N THE ELECTROPLATING AND METAL FINISHING INDUSTRIES

Today, t h e r e a r e between 1 5 , 0 0 0 and 20 ,000 f a c i l i t i e s i n the United States which e i t h e r wholly or p a r t i a l l y engage i n e l e c t r o - p l a t i n g o r o t h e r metal f i n i s h i n g operat ions. In order t o improve the sur face and s t r u c t u r a l sur face p rope r t i e s of metals and o t h e r materials, t he p l a t i n g indus t ry makes use of many chemical and electrochemical reac t ions , producing e f f l u e n t s which a r e highly t o x i c and corrosive. Treatment c o s t s f o r e f f l u e n t waste a r e in- c reas ing , discharge requirements a r e becoming more s t r i n g e n t , and urbanizat ion increas ingly l i m i t s t he a v a i l a b i l i t y f o r dumping pur- poses and waste l a n d f i l l s . Thus, t h e r e a r e many problems t o be d e a l t wi th i n handling t h e i n d u s t r y ' s waste.

Recent advances i n technology have produced a g r e a t p o t e n t i a l f o r water and metallic resource recovery. However, many firms con- t i n u e t o simply d i l u t e t h e i r wastestream and dump it i n t o the sew- er , sending an estimated 2 4 , 0 0 0 tons of metals worth approximately $ 4 0 mi l l ion down the d ra in each year . The tough economic condi- t i o n s of t he 1 9 8 0 s r equ i r e s t h e e l imina t ion of such ine f f i c i ency and waste.

The new methods of p l a t i n g waste c o n t r o l s which a r e being rea- d i l y accepted and implemented are founded on t h e philosophy t h a t the qu ickes t , e a s i e s t and cheapest w a y t o keep down pol lu t ion con- t r o l c o s t s i s n d t t o p o l l u t e i n the first place. many p l a t e r s are discovering t h a t e l imina t ion of end-of-line treat-

- - - - Q u i t e simply, --t - _I--

ment is the key t o important savings of c a p i t a l and operat ing c o s t s . In conjunction with t h i s philosophy, a few simple process adapta- t i o n s and technica l advances i n resource recovery which reduce t h e e f f l u e n t load and r e t a i n valuable p l a t i n g chemicals w i l l be ex-

' plored.

References : Cherry, Kenneth F. , P l a t i n Waste Treatment [Ann Arbor, Michigan:

/ Ann Arbor Science --Ti? Pu ishers, 19821.

EPA, Economics of Wastewater Treatment A l t e rna t ives f o r the Electro- -- p l a t i n q Industry, EPA-625/5-79-016, June 1979.

Quest ions: [ l l Explain the s ign i f i cance of t h e following quote which appeared on an SCA Chemical Services b u l l e t i n : "Any i n d u s t r i a l i z e d soc ie ty committed t o product iv i ty f o r a b e t t e r l i f e must f i nd new and b e t t e r ways t o dispose of t he by-products of i t s growing i n d u s t r i a l matur i ty ."

Does t h e slogan "Pol lu t ion Prevention Pays" hold t r u e f o r the e l e c t r o p l a t i n g industry?

, [2l Support your view w i t h examples.

POLLUTION PREVENTION ALTERNATIVES IN THE ELECTROPLATING AND METAL FINISHING INDUSTRIES

Quint M. Barefoot North Carolina State University

University Studies 495-B April 25, 1983

Elec t rop la t ing i s the production of a t h i n sur face coa t ing

of one metal on another by the process of e l ec t rod i spos i t i on .

This is achieved by passing an electric cu r ren t through a p l a t i n g

so lu t ion , thereby forc ing t h e m e t a l l i c ions i n the so lu t ion t o

t i g h t l y adhere t o one of the e l ec t rodes . Idea l ly , t he e l ec t rode

t o which t h e metallic ions c l i n g i s the i t e m being p la ted .

e l e c t r o p l a t i n g of common metals inc ludes the processes i n which a

nonferrous o r f e r rous b a s i s ma te r i a l i s e l ec t rop la t ed with copper,

n i c k e l , chromium, brass , bronze, z inc , t i n , l ead cadmium, i ron ,

aluminum o r combinations thereof . Precious metals e l e c t r o p l a t i n g

includes t h e processes i n which a nonferrous o r fe r rous b a s i s ma-

ter ia l i s e l e c t r o p l a t e d with gold, si lver, palladium, platinum,

rhodium, indium, ruthenium, i r idium, o s m i u m or combinations there-

of [l]. The corresponding changes produced by this process en-

hance the value of the t r e a t e d i t e m by providing such improvements

a s cor ros ion r e s i s t ance , d u r a b i l i t y , e s t h e t i c appearance, and elec-

t r i ca l conduct iv i ty [2].

The

Today, t h e r e a r e between 1 5 , 0 0 0 and 2 0 , 0 0 0 f a c i l i t i e s i n t h e

United S t a t e s which e i t h e r wholly o r p a r t i a l l y engage i n e l e c t r o -

p l a t i n g o r o t h e r m e t a l f i n i s h i n g opera t ions [ 3 ] . In order t o i m -

prove t h e s t r u c t u r a l sur face and sur face p rope r t i e s of metals and

o t h e r ma te r i a l s , t h e p l a t i n g indus t ry makes use of a tremendous

amount of chemical and electrochemical r eac t ions , producing ef-

f l u e n t s which a r e highly t o x i c and corrosive.

e l e c t r o p l a t i n g run, the p ieces t o be p l a t ed are placed on conveyor

racks and are dipped i n a series of tanks i n which cleaning, etch-

ing , p l a t i n g and r i n s i n g so lu t ions are found. The excess process

chemical must be removed by r igorous washing a f t e r each s tage , and

"During a typ ica l

2

t h i s ac t ion

with ac ids ,

produces l a rge q u a n t i t i e s of wastewater contaminated

bases, cyanide, metals, b r ighteners , c leaners , o i l s ,

and d i r t " [41 . According t o f i g u r e s re leased i n Ju ly 1 9 8 2 , t h e

United S t a t e s Environmental Pro tec t ion Agency [EPAI revealed tha t

of the 34 i n d u s t r i e s covered by EPA's tox ic wastewater r egu la t ions ,

m e t a l f i n i s h e r s contr ibuted 57% of the metals released t o sewers

[ S I . E l ec t rop la t ing and metal f i n i s h i n g w a s t e streams are s i g n i -

f i c a n t con t r ibu to r s t o stream po l lu t ion , e i t h e r d i r e c t l y , owing

t o t h e i r conten t of t o x i c and co r ros ive m a t e r i a l s , o r i n d i r e c t l y ,

owing t o t h e de l e t e r ious e f f e c t these components e x e r t on sewage

t reatment systems.

Un t i l r ecen t ly , t h e major 'waste concern has been the destruc- I

t i o n and removal of t he more deadly tox ins such as cyanide and hexa- I I

J v a l e n t chromium, while ignoring the presence of add i t iona l pollu-

t a n t s such as phosphates, phenols, heavy metals, o i l and pH f luc -

t u a t i o n s [ 6 ] . Batch discharges of t hese ma te r i a l s from a p l a t i n g

p l a n t can completely des t roy the b i o l o g i c a l f l o c of a municipal

t reatment p l an t . Rela t ive ly small volumes of such waste can wipe

o u t the aqua t i c l i f e i n a l a r g e stream. Q u a n t i t i e s a s small a s 1 ppm

i s s u f f i c i e n t t o k i l l f i s h [71.

However, environmental concerns should n o t serve as the only

incen t ive for examining t h e wastewater stream of the e l e c t r o p l a t i n g

indus t ry . Waste d i sposa l , t reatment and t ranspor ta t ion a re esca-

l a t i n g a t phenominal r a t e s .

dus t ry t o quest ion the v a l i d i t y of using v a s t q u a n t i t i e s of f r e sh

water f o r r i n s e processes. Moreover, t h e waste sludge contains

high volumes of common e l e c t r o p l a t i n g chemicals such a s cyanide,

Rising water c o s t s have forced the in-

t

3

chromium, n i c k e l , cadmium, and zinc; a l l which have r i s e n i n c o s t s

50 to 150% s i n c e 1972 [see F I G U R E 1 3 .

Recent advances i n technology have produced a g r e a t p o t e n t i a l

f o r water and m e t a l l i c resource recovery. However, an American

s tudy concluded t h a t about 90% of f i rms use a simple de tox i f i ca t ion

and d isposa l treatment on t h e i r waste r a t h e r than any type of re-

source recovery. Many f i rms simply d i l u t e t h e i r wastestream and

dump it i n the sewer system, sending v a s t q u a n t i t i e s of copper, nic-

k e l , chromium and zinc down the d ra in .

t h a t f o r each pound of metal t h a t l eaves t h e p l a n t p la ted on an au-

tomotive r i m o r p iece of galvanized steel, 9 pounds leaves a s a

sludge i n the w a s t e w a t e r stream 191. I n the United States alone,

2 4 , 0 0 0 t ons o f m e t a l s , worth approximately $40 mi l l i on , are d i sca r -

ded by e l e c t r o p l a t e r s each year [lo]. An i ndus t ry consul tan t re-

c e n t l y es t imated t h a t it would be t e c h n i c a l l y f e a s i b l e t o recover

about 30 t o 40% of the zinc, 70 t o 75% of the chromium, 80 t o 90%

of t h e copper and 90 t o 95% of t h e n i cke l c u r r e n t l y being poured

down the d r a i n o r trucked t o l a n d f i l l s i tes as sludge [ill.

A r ecen t study revealed

The conventional t reatment of e l e c t r o p l a t i n g wastewater i m -

p u r i t i e s takes place a t t h e end-of-line and involves treatment of

l a r g e volumes of wastewater by chemica l 'p rec ip i ta t ion . The addi-

t i o n of chemicals r e a c t with soluble p o l l u t a n t s producing inso luble

byproducts. The byproducts sett le, t h e w a t e r removed t o the sewer,

and the sludge thickened before dumping i n a convenient l a n d f i l l

s i t e [see F I G U R E 21 .

This opera t ion e n t a i l s l a r g e c a p i t a l c o s t s and produces v a s t

volumes of metal containing sludges. A w a t e r po l lu t ion problem i s

Item 1972 cost 1978 cost

Plating chemicals ($/lb):asb

. . . . . . . . . Zinc (as Zn metal)' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Zinc cyanide (Zn(CN),)'. . . . . . . . . . . . . . . . . . . . . , , , , . . , . ,

Water pollution control chemicals Calcium hydroxide (Ca(OH)2) . . . . . . . . . . . . . . . . . . . . . . . . . . . Calcium oxide (CaO) quicklime.. . . . . . . . . . . . . . .

. . . . . . . . . . . . ............................

Hydrochloric aci ............................. Sodium bisulfite Sodium carbonat . ......... Sodium hydroxid uivalent) . . . . . . . . . . . . . . . . Sodium hypochlorite (NaOCI) . . . . . . . . . . . . . . . . . . . . . . . . . . . Sodium sulfide (Na,S). . . . . . . . . . , . . . . . . .

. . . . . . . . .

Sulfur dioxide (SO,). .................... Sulfuric acid (H,SO,) . . . . . . . . . . . . . . . . . . . . . . . .

Electricity ($/kWh). . . . . . . . . . . . . . . . . Steam by energy sou I:

Utilities:d

Natural gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oil . . . . . . . . . . . . . . . . Use fee ............................... Sewer fee' . . . . . . . . .

Water ($/l,OOO gal):

0.069

0.37 1.05 0.47 0.67 0.50 0.2 1 0.1 8 0.64

-

0.01 0 0.009 0.038

0.01 35 0.066 0.01.8 0.036

0.07 0.038 0.01 7

-

-

0.028

1.03 1.39

0.25 0.25

0.1 76 2.60 0.78 1.95 0.88 1.04 0.76 0.40 0.31 1.41

0.01 7 0.01 6 0.075 0.40 0.023 0.13 0.03 0.08 0.40 0.12 0.085 0.023

0.045

2.07 3.53

0.50 0.60

'Prices are for bulk shipments of chemicals; prices for smaller quantities or especially pack- aged quantities may be 10% to 50% higher. Plating chemicals purchased with proprietary additives are from 20% to 40% higher.

bPrices from Chemical Marketing Repofler, Oct. 30, 1972. and Feb. 20. 1978.

'Substance is on list of EPAs 131 priority pollutants.

dAverage prices.

"Typical of a metropolitan area.

CHROMIUM REDUCTION n

Acid/alkai, 1 r!f waste

I I I CI, Caustic

Polymer

SLUUGE (thickeninc STORAGE

I ' NEUTRALIZATION

Leaend a-= sulfonator

= chlorinator

4

simply transformed i n t o a s o l i d waste d i sposa l problem.

of s o l i d waste d isposa l has increased an average of 500% during the

p a s t four years.

l e g i s l a t i o n which p r o h i b i t s a l l metallic sludge f r o m being placed i n

chemical l a n d f i l l s i n an attempt t o l i m i t i t s p o t e n t i a l t o contami-

The costs

N e w Jersey and Ca l i fo rn ia have r ecen t ly passed

n a t e gro'und water suppl ies . I t i s predic ted t h a t many more states

w i l l soon follow with s i m i l a r l e g i s l a t i o n .

Within the next few years , new and s t r i n g e n t environmental re-

gu la t ions w i l l come i n t o e f f e c t f o r t h e e l e c t r o p l a t i n g and m e t a l

f i n i s h i n g indus t r i e s . These r egu la t ions , promulgated on t h e l o c a l

and na t iona l l e v e l , p a r t i c u l a r l y by the EPA, has confronted t h e

e l e c t r o p l a t i n g indus t ry with a mult i tude of po l lu t ion con t ro l re-

quirements forwas.tewater and s o l i d res idues . In 1 9 7 9 , EPA estima-

t ed t h a t up t o 20% of a l l e l e c t r o p l a t i n g f i r m s may close due t o

wastewater requirements alone [12].

Fortunately, new developments i n resource recovery technology

allowed inexpensive improvements and adapta t ions which e l imina te

moat of t h e e l e c t r o p l a t e r s ' previous waste and inef f ic iency . These

techniques enable p l a t i n g shops t o avoid the majori ty of t he waste-

w a t e r t reatment c o s t s o r i g i n a l l y es t imated by the EPA. Furthermore,

many of these techniques and adapta t ions a c t u a l l y pay f o r themselves

i n a s h o r t period of t i m e , thereby o f f e r i n g e l e c t r o p l a t e r s increas-

i ng ly a t t r a c t i v e economic incen t ives to implement such changes.

The new methods of p l a t i n g waste con t ro l s which a r e being rea-

d i l y accepted and implemented are founded on the philosophy t h a t

5

many p l a t e r s a r e discovering

ment is the key to important

t h a t e l imina t ion of end-of-line t r e a t -

savings of c a p i t a l and opera t ing costs.

Incorporat ing t h i s philosophy, a few simple process adapta t ions and

t echn ica l advances i n resource recovery which reduce the e f f l u e n t

load and r e t a i n valuable p l a t i n g chemicals w i l l be explored.

Water is a major ma te r i a l i n t h e metal f i n i s h i n g indus t ry and

i s a s soc ia t ed with every process. Rinsing r ep resen t s t he m o s t f r e -

quent ly used process. It i s by f a r t h e l a r g e s t consumer of w a t e r ,

and has been given l i t t l e cons idera t ion as a c o s t o r problem area .

A v a i l a b i l i t y , limitless suppl ies , and l o w cost have h i s t o r i c a l l y

cont r ibu ted t o negligence with r e spec t to p l a n t water usage and

good r i n s i n g techniques. Contr ibut ing t o t h i s a t t i t u d e was the

absence of any s t r i c t l y enforced res t r ic t ions on discharge of waste-

w a t e r . Rinsing d i f f i c u l t i e s were always overcome by addi t ion of

more wastewater; where t h e water went af terwards was of no impor-

tance.

Today, t he environment demands a t t e n t i o n ; t he re fo re , w a t e r

usage and e f f l u e n t q u a l i t y have become major f a c t o r s i n p r o f i t and

loss statements. Modern e f f l u e n t r egu la t ions have el iminated any

remaining p o s s i b i l i t y of cont inuing t o discharge untreated water.

In p l a n t modif icat ions t o p l a t i n g baths and r i n s e systems can re-

duce p o l l u t a n t loading by decreasing w a s t e w a t e r flowrates, thereby

improving raw material y i e l d s and reducing po l lu t ion con t ro l c o s t s .

The following methods a r e c o s t - e f f e c t i v e a l t e r n a t i v e s t o end-of-

pipe wastewater t reatment and are n o t beyond the economic reach of

m o s t smaller f i r m s .

Implementing a successful housekeeping program is of extreme

6

importance and r equ i r e s l i t t l e o r no c a p i t a l investment. If a

f i r m can prevent the loss of concentrated so lu t ions of p l a t i n g

chemicals, t h e savings i n raw material and wastewater t reatment

are q u i t e s i g n i f i c a n t [see FIGURE 31. Routine su rve i l l ance pro-

cedures must be implemented to in su re the success of a "good

house keeping 'I

E4 1

E5 1

program. Correct ive a c t i o n s should include :

Repair leads around processing equip- ment [ tanks, valves , pump seals, t r ans - f e r l i n e s , heat ing c o i l s , e tc . ] . Losses of 2 gal . /hr . [7.61/hr.] can occur e a s i l y through leaking pump seals alone.

I n s t a l l an t i s iphon devices , equipped with se l f - c los ing valves , on i n l e t water l i n e s where warranted.

Inspec t tank and tank l i n e r s pe r iod ica l ly to avoid f a i l u r e s t h a t might severe ly overload t h e waste treatment sys tem.

Inspec t p l a t i n g racks f requent ly f o r loose i n s u l a t i o n t h a t would cause excessive drag- o u t of p l a t i n g so lu t ions .

Ensure t h a t cyanide s o l u t i o n s do n o t mix with compounds [ i ron , n i c k e l ] t h a t would form d i f f i c u l t - t o - t r e a t waste.

U s e d ry cleanup, where poss ib l e , i n s t ead of rou t ine f looding with water.

I n s t a l l d r i p t r a y s and sp lash guards where required [ 1 4 1 .

Major savings i n sewer f e e s , treatment chemicals and invest-

ment costs f o r wastewater t reatment are achievable by simply mini-

mizing water usage.

[as much as 9 0 % ] of water, it possesses the g r e a t e s t p o t e n t i a l f o r

conservation. Rinsing i s used to d i l u t e t he concentrat ion of con-

taminants adhering t o t h e workplace to ensure t h a t the so lu t ion i n

the next process tank w i l l be e f f e c t i v e and remain uncontaminated.

Since the r i n s i n g process is t h e major consumer

Note.-Basis: Operating 4,800 hlyr. Costs from Table 1 and Figures 12 and 13.

I 1 1 2 3 4 0 1

LEAKAGE RATE (gal/h)

Legend: A = chromic acid plating solution 34% H2Cr0, B = 93% H,SO, C = acid copper plating solution: CuSO,,

10 oz/gal: H,SO,, 25 oz/gal D = 50% NaOH (replacement cost only) E = zinc cyanide solution: zinc (as metal),

30 oz/gal: NaCN. 6 orlgal: NaOH, 12 ozlgal

C

7

any e l e c t r o p l a t i n g shops s t i l l employ s i n g l e , flowthrough r i n s e

tanks t o remove t h e s o l i d s and c l ing ing dissolved sal ts from work

pieces . This method of r i n s i n g i s extremely i n e f f i c i e n t , and f o r

a t y p i c a l p l a t i n g shop, r e s u l t s i n the generation of thousands of

ga l lons of contaminated r i n s e water per day.

The counter cu r ren t concept of r i n s e f l o w can be u t i l i z e d suc-

c e s s f u l l y t o s u b s t a n t i a l l y reduce the amount of wastewater genera-

t ed a t a p l a t i n g shop. The b a s i c concept of counter cu r ren t opera-

t i o n i s t o use water from previous r i n s i n g s t o contac t t he more

contaminated work a r t i c l e [see FIGURE 41. For example, a 33-ounce-

to-the-gallon bath is r i n s e d to t h e standard of 0 . 0 0 1 ounce t o t h e

gal lon. I n order f o r four ga l lons of excess p l a t i n g material to be

ex t r ac t ed o u t of t h e bath and washed clean [ i .e. , 4 gal lons per

hour drag-out] , t he following amount of r insewater i s required:

Single Rinse Tank 2 Tank Counter-Flow 3 Tank Counter-Flow 4 Tank Counter-Flow 5 Tank Counter-Flow

132,000 Gal./Hr. 740 G a l . / H r . 126 Gal./Hr. 53 Gal./Hr. 32 Gal./Hr. [151

On a t y p i c a l e l e c t r o p l a t i n g l i n e , t h e r e a r e probably ten r i n s e

systems following the p l a t i n g and e tch ing baths . The use of f i v e

r i n s e counter-flow tanks in s t ead of one reduces the hourly produc-

t i o n of w a s t e w a t e r from 1.3 m i l l i o n ga l lons t o only 320 gal lons.

However, it must be noted t h a t t h i s wastewater, regard less of t h e i r

tremendous d i f f e rences i n volume, s t i l l contain ident icak me ta l l i c

loads.

V a s t q u a n t i t i e s of w a t e r may a l s o be conserved through reac-

t i v e r in s ing . T h i s technique simply allows f o r t he r euse o r recycle

1 - - - - - - - - - - - -)L Part,. t. 1

I I I 1 I I I I I I I

I I I

To wastewatet treat m R n t

7- Rinse rei fet.ri -

- 1 Air

Spent rinse water

ing / l i

No of rinse stages

I * a n l d ~ pipe\ Air auitation Rinse ratio rcncentratcon

1 1,000 3 7 2 100 370 3 10 3, ?OQ 4 6 6,: 70

'Required to maintain concentration in final rinse at 3 ) mg/i if the drag-out conceqtrstion equ3ls 37.000 m g / i

THREE-STAGE COIJNTERCLRRFR;; '<!PIS5 WITH 3UT90ARD ARRANGEMENT

a

of r i n s e water one o r more t i m e s before it is discharged by taking

advantage of t he chemical r e a c t i v i t y of the used r i n s e water. Rin-

s ing e f f i c i e n c y can a c t u a l l y be increased, thereby improving p l a t -

ing q u a l i t y .

In t raprocess reactive r i n s i n g may be i l l u s t r a t e d by a n a l y s i s

of a t y p i c a l n i cke l p l a t i n g l i n e . The process i s composed o f :

[ll an a l k a l i n e cleaning tank. [21 an ac id d r i p tank, and [31 a n i cke l p l a t i n g tank [see FIGURE 51.

Each process s t e p is followed by a running r i n s e tank, with each

having a separa te f reshwater feed l i n e . In t h e course of an e ight -

hour work day, t h i s s i n g l e p l a t i n g process accounts f o r 5 , 7 0 0 gal-

lons of w a t e r .

The p a r t t o be p l a t ed "drags-in" t o the n i cke l tank whatever

substance which w a s i n t h e previous tank. I f t h a t r i n s e tank is

fed with f r e s h w a t e r , t h e drag-in w i l l mostly c o n s i s t of a d i l u t e

ac id so lu t ion which reduces both t h e n i cke l concentrat ion, and t o

some e x t e n t , t he a c i d i t y of t h e process bath. The ac id r i n s e tank

could be fed w i t h t h e discharge from t h e n i cke l r i n s e tank a s a

replacement f o r the f r e s h w a t e r feed. Since t h e n i cke l r i n s e tank

conta ins d i l u t e process so lu t ion , it w i l l feed the acid r i n s e tank

with a c i d i c water containing process so lu t ion and n i c k e l salts.

Likewise, the drag-in from the ac id r i n s e tank w i l l p a r t i a l l y re-

p l en i sh chemicals i n the n i c k e l tank. Nickel r i n s e water does n o t

harm t h e r i n s i n g s t e p a f t e r t h e a c i d bath, and it a i d s i n conser-

va t ion of chemicals i n t h e n i c k e l p l a t i n g bath w h i l e allowing the

f r e s h water feed l i n e t o the ac id r i n s e tank t o be turned o f f , sav-

ing 4 gpm. This example of r e a c t i v e r i n s i n g reduces water

. I

F I G U R E 5 : I N T R A P R O C E S S R E A C T I V E R I N S I N G

--- RCUC Flow Scheme

SOURCE: SALTZBERG,EDWARD R. ,A MANUAL OF NEW;' \WASTE

Cost (Silbl

Replacement Treatment' DisposalL Total Chemical

Nickel As NISO, 0 76 o 2a 0 1 7 1 2 1

1 0 4 0 29 0 2 4 1 5 7 As NiCI,

Using CI, for cyanide oxida-

Using NaOCl fcr cyanide oxida-

Zinc cyanide as Zn(CN)>

tion 1 4 1 0 72 0 2 5 2 3 8

tion 1 4 1 1 5 3 0 2 5 3 1 9 Chromic acid as H2Cr0,

Using SO., for chromium reduc-

Using NaHSO, for chromium tion 0 78 0 4 8 0 3 2 1 5 8

reduction 0 78 0 6 9 0 3 2 1 7 9

Using CI, for cyanide oxidation 1 9 5 0 72 0 2 5 2 9 2 Using NaOCl for cyanide oxida-

tion 1 95 1 5 3 0 2 5 3 7 3

Copper cyanide as Cu(CN)?

Copper sulfate as CuSO, 0 56 0 28 0 1 7 101 ~ ~-

"Based on treatment model presented in Figure 1 2 at a concentrat\on of 100mg~l in wastewater

"Based on Figure 13

9

consumption, and saves process chemicals without harming t h e r i n s e

s t e p [16].

Reactive r i n s i n g is n o t expensive. I t i s a very e f f e c t i v e a l -

t e r n a t i v e t o counterflow r i n s i n g without t h e cost o r l o g i s t i c a l

cons t r a in t s . Since it requ i r e s no a d d i t i o n a l r i n s e tanks, it can

e a s i l y be used i n p l a t i n g shops where the re is no space f o r p l a n t

expansion.

Dras t i ca l ly reducing the amount of wastewater by no means so lves

a l l the hazardous and economic a i lments of t h e p l a t i n g indus t ry .

Extremely high m e t a l l i c and chemical concent ra t ions s t i l l e x i s t in

s m a l l amounts of wastewater. Therefore, recovery methods must be

implemented t o ease t h e burden of replacement and d i sposa l expenses

[see TABLE 1 1 . "Recovery techniques are t reatment methods used f o r

the purpose of recovering o r regenera t ing process cons t i t uen t s which

would otherwise be l o s t i n the wastewater o r discarded" [171. These

processes a l l opera te on t h e same b a s i c p r i n c i p l e ; they concentrate

the dragged-out p l a t i n g s o l u t i o n i n the r i n s e water t o the po in t

t h a t t he so lu t ion can be s a f e l y returned to the p l a t i n g bath. The

volume of r i n s e w a t e r must be reduced to a quan t i ty t h a t can be eco-

nomically processed i n o rde r t o use a recovery un i t . Recovery pro-

cesses include evaporation, reverse osmosis, ion exchange and re-

c e n t l y e l e c t r o d i a l y s i s . The economics of some of t he more innova-

t i v e recovery technologies favor t h e l a r g e r p l a t e r and may present-

l y be o u t of t he reach of some smaller f i r m s .

The f i r s t separa t ion technique to recover p l a t i n g chemicals

l o s t t o r i n s e streams w a s evaporation. The process has been suc-

c e s s f u l on v i r t u a l l y a l l types of p l a t i n g baths . Recovery i s

10

accomplished by allowing the evaporator or boi ler port ion of the

system t o c o l l e c t t he contaminated r i n s e water. Ins ide , a steam

c o i l b o i l s o f f the water t o a vapor and the concentrat ion of t h e

so lu t ion continues u n t i l it reaches t h e des i r ed dens i ty . The ma-

t e r i a l s of cons t ruc t ion a r e compatible with the so lu t ion . The con-

densed steam provides a continuous flow of d i s t i l l e d water, inde-

pendent of so lu t ion processing. Automatic, c losed loop systems

opera te continuously i n extremely cor ros ive environments w i t h

vacuum evaporation allowing the so lu t ion t o b o i l a t l o w tempera-

t u r e s [102°-1400F. ] , saving energy and e l imina t ing chemical break-

down. T o t a l i n s t a l l e d investment, opera t ing costs, and economics

f o r i n s t a l l i n g a 20 gal . /hr . [76 c/h] Chromic Acid Evaporative Re-

covery Unit i s given i n TABLE 2 . The t o t a l annual savings includ-

ing recovered p l a t i n g chemicals, water t reatment chemicals, sludge

d i sposa l and water use amounted t o $ 1 4 , 8 8 0 . This r e s u l t e d i n an

average payback per iod of 7.9 years .

Reverse osmosis [ROI i s the separa t ion of one component of a

s o l u t i o n from another component by means of exe r t ing pressure on a

semipermeable membrane. The RO membrane which serves a s a " f i l t e r

ma te r i a l " i s a c t u a l l y a c e l l u l o s e acetate f i l m - - a mater ia l much l i k e

cellophane which is used to wrap foods. The membrane f i l t e r ma-

t e r i a l has a multi tude of sub-microscopic pores [0.0005 t o 0 .002 m i -

c rons] which enable it t o f i l t e r o u t t h e same ma te r i a l s as a stan-

dard mechanical f i l t e r as w e l l a s t h e sal ts and organics which a r e

chemically dissolved i n t h e w a t e r . A s the feed so lu t ion moves

across t h e membrane, t h e permeate is removed [ f i l t e r e d so lu t ion ] , and the s o l u t e s o r dissolved p a r t i c l e s i n the feed a r e concentrated

Item cost

Installed cost. 20-gal/h evaporator ($): Equipment:

Evaporator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pumps . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................... Cation exchanger. . . . .................................. Piping . . . . . . . . . . . . . . . . . . . ......................................... Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . ...................................

Installation. labor and materials: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Plumbing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........................................ Electrical. . . . . . . . . . . . . . . . . . . . . . . . Equipment erection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..............................

Subtotal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Total installed cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .................... Annual operating cost ($/yr):

Labor, 100 h/yr a t$7/h ...................................................................................... SupeNision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........................................ Maintenance, 6% of investment. . . . . . . . . . . . ............................. . . . . . General plant overhead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Raw materials, cation exchanger:

Electricity, $0.045/kWh . . . . .

Total operating cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Annual fixed costs ($/yr): Depreciation, 10% of investment. . ......................... Taxes and insurances, 1 % of investment. . . . . . . . . . . . . .

.......................

Total fixed costs.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..........................

Total costs of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Annual savings ($/yr): Recovered plating chemicals, (1 .E75 Ib/h H2Cr0,. Water treatment chemicals. . . . . . . . . . . . . . . . . . . . Sludge disposal ............................. Water use, 13 gal/h at 1.10/1 ,000 gal . . . . . . . . . .

Total annual savings ....................... .......................

Net savings Net savings after taxes, 48% tax rate ($/yr) . . . . . . . . . . Average ROI = (net savings after taxes/total investment) X 100 (%). ................................................... Cash flow from investment = net savings after taxes + depreciation ($/yr) .......................................... Payback period = total investment/cash flow (yr) ...................................................................

annual savings - (operating cost + fixed cost) ($/yr). . . . . . . . . . . . . . .

19,000 1,660

750 6.200 2,500

450

30,560

260 2.860 1.230

270 500

5.120

35.680 -

700

2,190 880

1 0 0 240

1,400 500

3.1 50

("1

9.1 60

3.570 360

3,930

13.090

7.31 0 4,500 3,000

70

14,880

1,790 930

4,500 2.6

7.9 ~~

'None required.

bFrom Table 10, based on a 90% operating factor.

Note.-If the evaporator installation had eliminated the need for a chromium reduction system, a $1 7,000 investment in treatment hardware would have been avoided. In this case, the additional investment for the evaporator would have an after-tax average ROI of 10.2%. and the payback would b e 4.9 yr.

11

i n t o a reduced

Theore t i ca l ly ,

volume of so lu t ion referred to as the concentrate .

such systems recover 99% of p l a t i n g chemicals l o s t

t o the r i n s e system. The major l i m i t a t i o n of RO systems is the in-

a b i l i t y t o maintain s u f f i c i e n t membrane performance.

feed s o l u t i o n s must maintain a p H range between 2 . 5 and 11 to en-

sure proper performance and reasonable membrane l i f e .

the system itemized i n TABLE 3 , amounts to $19,500 with a payback

per iod of 4.3 years.

Present ly ,

The c o s t of

Ion exchange is a v e r s a t i l e separa t ion process with tremendous

p o t e n t i a l i n t he p l a t i n g indus t ry , both f o r raw material recovery

and reuse and f o r water po l lu t ion con t ro l .

mical s o l u t i o n i s passed through a bed of r e s i n , thus s e l e c t i v e l y +2 -2

removing both c a t i o n s [e.g., Cu , Fe+2] and anions [e.g. , C r 0 4 , CN-1 from t h e so lu t ion . The removal is accomplished by exchanging

an ion from the su r face of a r e s i n p a r t i c l e f o r a s i m i l a r l y charged

ion i n t h e so lu t ion .

s o l u t i o n s and the t r e a t e d water i s extremely pure. The f a c t t h a t

t he r e s i n must be regenerated a f t e r it has exhausted i t s exchange

capac i ty i s a major drawback.

volumes of wash so lu t ion which adds t o the waste t rea tment loading.

The t o t a l c o s t of i n s t a l l a t i o n f o r an ion exchange system i s $31,000

with annual savings amounting to $14,320 [see TABLE 4 1 .

provides a payback per iod of 5 . 2 years.

In ion exchange, a che-

Ion exchange i s i d e a l l y s u i t e d for d i l u t e

This l i m i t a t i o n r e s u l t s i n small

The system

Concentration or separa t ion of i o n i c spec ies contained i n w a t e r

i s known as e l e c t r o d i a l y s i s . T h i s new process is w e l l e s t ab l i shed

f o r pur i fy ing brackish w a t e r , and has r ecen t ly been shown t o exhi-

b i t e x c e l l e n t recovery p o t e n t i a l f o r metal s a l t s i n p l a t i n g r in se .

Item cost

Installed cost, 330-ft2 unit ($): Equipment:

RO module including 50-pm filter, pump, and 6 membrane modules at 55 h2 per module. . . . Activated carbon filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Piping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Subtotal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Installation. labor and material: Site preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plumbing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Electrical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Subtotal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Total installed cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Annual operating cost ($/yr): Labor, 100 h/yr at $7.00/h.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General plant overhead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Raw materials:

Supervision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Module replacement, 2-yr life (6 X $320)/(module X 0.5 yr) Resin for carbon filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Utilities, electricity (0.045/kWh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Total operating cost. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Annual fixed costs ($/yr): Depreciation, 10% of investment. . . . . . . . . . . . . . . . . . . Taxes and insurance, 1% of investment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Total fixed costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Total cost of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Annual savings ($/yr):b Plating chemicals:

1.65 lb/h NiSO, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . .

. . .

. . .

. . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . . . . . . . . . . . . .

. . .

. . .

. . . . . . . . . . . . . . . . .

. . .

. . . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

. . . 0.34Ib/h NiCI - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . .

. . . . ' Water treatment chemicals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sludge disposal cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Water use (no saving) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Total annual savings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Net savings = annual savings - (operating cost -I- fixed cost) ($/yr)

Average ROI = (net savings after taxes/total investment) X 100 (%). Cash flow from investment = net savings after ta Payback period = total investment/cash flow (yr) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Net savings after taxes, 48% tax rate, 4,915 X 0.52 ($/yr). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

15,000 2.000 500 500

18,000

200 300 500 500

1.500

19,500

700

1,170 660

(7

960 500 510

4,500

1,950 200

2.1 50

6,650

5.640 1,590 2.520 1,810 -

11.560

4.91 0 2,550

13 4,500

4.3 ~

'None required.

'From Table 10. based on a 90% operating factor.

Item cost

Installed cost ($): Equipment:

Reciprocating flow ion exchanger. including cartridge filter and three ion exchanger beds. . . . . . . . . . . . . . . . . . . . . . . . . 28,500 Piping . . . . . . . . . . . . . . . . . . . . . . . . . . Miscellaneous . . . . . . . . . . . . . . . . . . .

Subtotal . . . . . . . . . . . . . . . . . . . . . . . . . . .

Installation, labor and material: Site preparation . . . . . . . . . . . . . . . . . . Plumbing. . . . . . . . . . . . . . . . . . . . . . . . Electrical . ....................... Miscellaneous . . . . . . . . . . . . . . . . . . .

Subtotal. . . . . . . . . . . . . . . . . . . . . . . . . . .

Total installed cost . . . . . . . . . .

Annual operating cost ($/yr): Labor, 100 h/yr at $7.00/h.. . . . . . . . . . . . Supervision . . . . . . . . . . . . . . . . . . . . . . . . . . Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . General plant overhead. . . . . . . . . . . . . . . . Raw materials:

Replacement resin, . . . . . . . . . . . . . . . Regeneration chemicals:

. .

. .

. .

. .

. .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

NaOH. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H,SO,. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Utilities, compressed air . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Total operating cost.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Annual fixed costs ($/yr): Depreciation, 10% of investment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Taxes and insurance, 1 % of investment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

500 500

29.500 - 200 300 500 500

1.500

31,000

700

1,860 800

500

(a)

680 670 200

5,410

3.100 310

Total fixed cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.41 0

Total cost of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8,820

Annual savings ($/yr)? Plating chemicals, 2 Ib/h H2Cr0, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7,020 Water treatment chemicals.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........................ 4,320 Sludge disposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2,880 Water use, 18 gal/h at$1.10/1,000 gal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0 0

Total annual savings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14,320

Net savings = annual savings - (operating cost + fixed cost) ($/yr

Cash flow from investment = net savings after taxes + depreciatio

.................... 5,500 2.860

.................... 5.960

Net savings after taxes, 48% tax rate ($/yr) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Average ROI (net savings after taxes/total investment) X 100 (%)

Payback period = total investment/cash flow (yr) . . . . . . . . . . . . . . .

'None required.

9.2

5.2

bFrom Table 10, based on a 90% operating factor.

, 1

12

In e l e c t r o d i a l y s i s , a w a t e r so lu t ion i s passed through several a l -

t e r n a t e l y placed ca t ion and anion permeable membranes. The ion

migration is i n i t i a t e d by an electrical p o t e n t i a l appl ied across

t h e membrane. Because ion migration is propor t iona l t o e lectr ical

p o t e n t i a l , t he optimum system is a trade-off between the cathode

and anode d i l u t i o n streams. Recent EPA s t u d i e s demonstrate the

wide a p p l i c a b i l i t y and extreme e f f i c i e n c y of the e l e c t r o d i a l y s i s

u n i t s . Total i n s t a l l a t i o n costs amount t o $27,500 with annual sav-

ings of $ 2 1 , 0 9 0 [see TABLE 51.

of 2 .8 years .

This r e s u l t s i n a payback per iod

Recently, many platers have experimented with t h e performance

of t r i v a l e n t chromium [Cr+3] versus hexavalent chromium [Cr+6] . The r e s u l t s have shown tri-chrome t o be a much more e f f i c i e n t pro-

duc t . Tri-chrome inc reases p ro tec t ion dramat ica l ly by depos i t ing

a microdiscontinuous p ro tec t ive coa t ing t o prevent corrosion. T r i -

chrome is less blue than hexavalent chromium y ie ld ing a softer f in -

i s h which blends b e t t e r with a wider range of colors and o t h e r f in -

i shes .

conventional hex-chrome t o tri-chrome. Lined tanks, spec ia l g raphi te

anodes, mild a i r a g i t a t i o n and cool ing f o r high volume production

and f i l t r a t i o n i s required. Although tri-chrome so lu t ion cos t s

a r e higher , o v e r a l l savings r e s u l t from increased production and

reduced w a s t e t reatment cos ts . B e s t of a l l , f i rms reduce sludge by

85% [see FIGUFtE 6, TABLE 61.

Only a few s m a l l changes a r e necessary i n the switch from

The technology is a v a i l a b l e and t h e economics are growing more

favorable for the i n t e g r a t i o n of po l lu t ion prevention p o l i c i e s i n

the e l e c t r o p l a t i n g f i e l d . P l a t i n g management must abandon o ld

Item cost

Installed cost ($): Equipment:

Electrodialysis unit, complete with cartridge filter strainer and electrode rinse system . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Installation. labor and material: Site preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Miscellaneous . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Subtotal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Total installed cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Annual operating cost (Wyr): Labor, 100 h/yr at$7.00/h . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S u p e ~ i s o r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . General plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Raw materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Filter cartridges . . . . . . . . . . . . . . . . . . . . . . . . . . ................................... Replacement membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....

. . . . . . .

. . . . . . . . . . . . . .

Utilities, electricity (0.045/kWh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Total operating cost. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Annual fixed costs ($/yr): Depreciation, 10% of investment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Taxes and insurance, 1 % of investment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

25.000 500 500

26,000

200 300 500 500

1,500

27.500 -

700

1.650 750

(*I

750 300 200

4,350

2.750 280

Total fixed costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3,030

Total cost of operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Annual savings ($/yr):b Plating chemicals, 3.8 Ib/h NiSO, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Water treatment chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sludge disposal cost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Water use(no saving) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Total annual savings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Net savings = annual savings - (operating cost + fixed cost) ($/yr). . . . . . . . . . . . . . . . . . . Net savings after taxes, 48% tax rate ($/yr) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cash flow from investment = net savings after taxes + depreciation ($/yr). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Payback period = total investment/cash flow (yr) .

Average ROI = (net savings after taxes/total investment) X 100 (%). . . . . . . . . .........................

7.380

13.250 4,880 2,960 -

21,090

13,710 7.130

26 9,880

2.8

aNone required.

bFrom Table 10, based on a 90% operating factor.

HEX-CHROME VS. TRI-CHROME: In a simple destruct system here's how Tri-Chrome compares with Hex-Chrome for chemicals needed and sludge generated.

1 HEXAVALENT CHROME

1 Gallon 2.9 Ib. Sodium 2.0 Ib. Sulfuric 2.7 Ib. Lime 32 oz.lgal. Bisulfite (anhydrous) Acid Chromic Acid

7.1 Ib.* Sludge Containing 4.9 Ib. Calzium Sulfate 2.2 Ib. Chromium Hydroxide

TRl-CH ROM E - - +6

1 Gallon 0.4 Ib. Lime I Ib. Sludge Containing 0.7 Ib. Calcium Sulfate 0.3 Ib. Chromium Hydroxide

Tr i -C h ro m e

1945 EAST 97th STREET CLEVELAND, OHIO 44106 1216) 731-830rl

'These volumes represent dry product. Actual sludge quantity would be significantly greater.

3 6 Cr vs. Cr Results As Observed At The Waste Treatment Plant

PROGRAM

Compare the effluent analysis of c w o similar electroplating companies. Company A used hexchrome in a Ni-Cr tubular frame plating operation until 1920, at which time they converted to tri-chrome, counter flowed rinse tanks, and installed drag-out tanks.

Company B began operation in 1982. Their plant was designed to plate tri-chrome.

Company A: Avg daily flow 45,OQQ - 513,001) gallons.

Hex Chrome 1974- 1980

Avq total chromium - 13.6 mg/l

Avg total nickel - 16.6 mg/l

Tri-chrome 1920 - present. Avg daily flow - 41),C)C)0 gallons.

Avg total chromium - 1-13 m g / l

Avg. total nickel - 6 . 3 m g / l

Company B: Tri-chrome 1932 - present. Avg total chromium - 2.2 mg/l

Avg total nickel - 1.5 mg/l

Edward Lawrence Industrial lJast e Chemist City of High Point P. 0 . Box 230 H i g h Point, NC 27261

d , "

13

a t t i t u d e s as w e l l a s d i sposa l techniques of the p a s t , and become

motivated t o e f f e c t i v e l y manage the resources t h a t are p resen t ly

wasted. I t is important t h a t t he business community recognize t h e

f i n a n c i a l oppor tun i t i e s inherent i n po l lu t ion prevention. "Although

tough new e f f l u e n t con t ro l s and r i s i n g c o s t s are s t rong incen t ives

t o c o n t r o l l i n g waste res idues , unless the management and staff

look on resource recovery as a viable business propos i t ion , it is

doomed t o wasteful i ne f f ec t iveness" [18].

14

REFERENCES

Cherry, Kenneth F . , P l a t i n g Waste Treatment [Ann Arbor, Michigan: Ann Arbor Science Publ ishers , 19821 , p. 3.

Watson, Michael R . , Po l lu t ion Cont ro l i n Metal F in ish ing [Park Ridge, New Jersey: Noyes Data Corporation, 19731 , p. 2.

S i t t i g , Marshall , E lec t rop la t ing - and Related Metal F in i sh in2 [Park Ridge, New Jersey: Noyes Data Corporation, 19781, p. 5.

Campbell, Monica E., and Glenn,William, P o l l u t i o n Preven- - t i on Pays [Ontario, Canada, P o l l u t i o n Probe Foundation], p. 41.

EPA, Assessment of the Impacts of I n d u s t r i a l Dischargers - on Publ ic ly Owned T r e a t G n t o r k s , N T I S N O . PB 82-153958, February, 1982.

S i t t i g , p. 2 .

' Ontario Minis t ry of t h e Environment, Metal Indus t r i e s : Manufacturing,Working, Finishing, Chapter X I 1 i n Control of In- d u s t r i a l Wastes i n Munic ipa l i t i es , I n d u s t r i a l Wastes Branch, On- t a r i o Minis t ry of t h e Environment, 1977 .

EPA, Economics of Wastewater Treatment Al t e rna t ives f o r - - t he E lec t rop la t ing Indus t ry , EPA-625/5-79-016, June 1 9 7 9 .

U . S . General Accounting Off ice , I n d u s t r i a l Wastes: An Unexplored Source of Valuable Minerals, Control ler Genera l ' sRe- port t o t h e Congress of t he United States, May 15, 1980.

lo Campbell, p. 43.

l1 U . S . General Accounting Off ice .

EPA, Economic Analysis of Proposed Pretreatment Standards 12 for E x i s t i n m - 2 d - 0 0 1 , December 1 9 7 7 .

Sources of t h e E lec t rop la t ing Poin t Source Category, -- l3 Sal tzberg , Edward R., A Manual of N e w Waste and Water Con-

servation and Reuse Methods f o r the E lec t rop la t ing Industry, 1983 Tr iangle Conference on Environmental Technology, Chapel H i l l , N . C.

-- - -- EPA, 625/5-79-016, p. 31.

.Campbell, p. 44.

Saltzberg, p . 1 0 . 1 6

Cherry, p. 4 5 . 1 7

l8 Campbell, p. 6 2 .

15